Sounds like the wax motor portion of the IAC is working properly.
There's an electric portion to the valve too, that works with the mechanical wax motor. There are a few things that will cause an idle up command to be sent - the AC system, electrical load control, and power steering pump have control authority over the IAC/BSC. There may be other systems that have influence as well
Have you disconnected the connector while it is running to see if there is a change in idle? (i am not sure if that is how these idle valves work, worth a shot though?)
There should be a section in the FSM for troubleshooting the IAC, but I am not sure how in-depth it is.